Most higher plants encounter at least transient decreases in relative water content at some stage of their life cycle and, as a result, have evolved a number of desiccation protection mechanisms. If however, the change in water deficit is prolonged the effects on the plant's growth and development can be profound. Decreased water content due to drought, cold or salt stresses can irreparably damage plant cells which in turn limits plant growth and crop productivity in agriculture.
Plants respond to adverse conditions of drought, salinity and cold with a variety of morphological and physiological changes. Although our understanding of plant tolerance mechanisms to these stresses is fragmentary, the plant hormone abscisic acid (ABA) has been proposed to be an essential mediator between environmental stimulus and plant responses. ABA levels increase in response to water deficits and exogenously applied ABA mimics many of the responses normally induced by water stress. Once ABA is synthesized it causes the closure of the leaf stomata thereby decreasing water loss through transpiration.
The identification of genes that transduce ABA into a cellular response opens the possibility of exploiting these regulators to enhance desiccation tolerance in crop species. In principle, these ABA signaling genes can be coupled with the appropriate controlling elements to allow optimal plant growth and development. Thus, not only would these genes allow the genetic tailoring of crops to withstand transitory environmental insults, they should also broaden the environments where traditional crops can be grown.
In addition, little is known of the genetic mechanisms which control plant growth and development. Genes which further affect other metabolic processes such as senescence and growth habits of plants can be useful in a wide variety of crop and horticultural plants.